An RCD or RCCB is a device that disconnects an associated load circuit whenever it detects that an electric current is leaking out of the circuit, such as current leaking to Earth through a ground fault. Such devices are intended to operate quickly so that when a person contacts a live conductor, the circuit is isolated before electric shock can drive the heart into ventricular fibrillation, which may cause death in such circumstances. Most RCD/RCCB devices are designed to trip when a leakage current that exceeds a threshold such as 30 mA (milliamps) is detected.
A significant problem with existing RCD/RCCB devices is a requirement that a good Earth to Neutral connection should be present for reliable and accurate operation of such devices. This means that great care and cost may be required to establish a “good” Earth connection. For example large building sites using electrically isolated power generators may require one winding of the generator to be connected to Earth and equipped with one or more RCDs. It also means that RCDs may have limited effectiveness in some parts of the world including those parts having sandy soils, such as the Middle East where it may be difficult to establish a good Earth connection.
The present invention may provide an improved safety device that may maintain protection against risk of electric shock in the event that the Earth to Neutral connection becomes excessively poor due to high resistance or discontinuity, or through a fault or other reason may cease to exist altogether, eg. when using an isolated power supply such as a generator. In such circumstances a safety device according to the present invention may provide a significant defense against risk of electric shock including in those parts of the world where it may be difficult to establish a good Earth connection.